How does an entity bean obtain a JTA UserTransaction object?

It doesn't. Entity beans do not employ JTA transactions; that is, entity beans always employ declarative, container-managed transaction demarcation. Entity beans, by definition, are somewhat tightly coupled (via the EJB container and server) to a datastore; hence, the EJB container is in the best position to manage transaction processing.

Advertiser Disclosure:
Some of the products that appear on this site are from companies from which QuinStreet receives compensation. This compensation may impact how and where products appear on this site including, for example, the order in which they appear. QuinStreet does not include all companies or all types of products available in the marketplace.